Abstract 12964: Over Expression of miR1 Leads to EAD Development in Cardiomyocytes by Increasing CaMKII and Calcium Current

Introduction: miR1 has been shown to induce cardiac arrhythmias in animal models but the mechanism is unclear. We overexpress miR1in rat cardiomyocytes and investigated the cellular mechanism of arrhythmia development. Methods: Rat cultured ventricular cardiomyocytes were infected with adenovirus-miR1 and adenovirus-GFP (control). Voltage and current clamp were used to record calcium current and action potentials at 35°C. Cells were loaded with Fura2-AM for measurement of calcium transients. Results: Action potential duration at 90% repolarization (APD 90 ) was 542.4% longer in ad-miR1 cardiomyocytes compared to control (377.1±137.2 ms vs. 58.7±7.2 ms vs., n=7, p 90 was due, in part, to a 174% increase in the incidence of early afterdepolarizations (EADs) in ad-miR1 cardiomyocytes (22±2 EADs/100 beats vs. 8±1 EADs/100 beats, n=25, P 2+ /calmodulin-dependent protein kinase II (CamKII) activation, we blocked CamKII with KN93 (1μ M) in ad-miR1 cardiomyocytes. Calcium current decreased from 18.7±0.7 pA/pF to 10.0±1.0 pA/pF, (n=11, p 90 (377.1±137.2 ms to 73.4±13.7 ms, n=11, p 90 decreased in ad-miR1 cells, but remained longer than in control cells (67.3±1.7 ms vs 18.8±1.6 ms, n=16 and 13, p 90 and that other currents may also involved in this prolongation in ad-miR1 infected cardiomyocytes. Conclusions: Overexpression of miR1 induced EADs in rat cardiomyocytes, in part, by increasing calcium current and CaMKII, which may be a mechanism of arrhythmias by miR1 overexpression in animal models.